▎ 摘　　要

We derive and analyze a 2D model for plasmons, in order to understand the general preconditions for the appearance of THz plasmons in low-dimensional nanosystems like graphene. Using experimental data and back of the envelope type calculations, we discuss the typical frequency ranges of plasmon resonances in such systems. Next we compare our results to recent ab initio calculations for ideal graphene, and show that these are consistent with the predictions of a 3D plasmon model, rather than a 2D model. The validity of the ab initio calculation does not extend to long-wavelength regime where our 2D model holds.